1. Field of the Invention
The present invention relates to an exposure data preparation method and an exposure method. In particular, it relates to an exposure data preparation method for preparing exposure data to be used in a charged particle beam exposure technology using an electron beam or an ion beam in a lithography procedure and an exposure method using the exposure data.
2. Description of the Related Art
In electron beam exposure for delineating a pattern by irradiating an electron beam on a resist applied on a substrate, not only forward scattering where some incident electrons scatter in the resist but also backscattering where some electrons passing through the resist are reflected from the substrate and re-enter the resist occurs. Accordingly, even when an incident electron beam is directed onto one point on the resist, scattering of the beam produces proximity effects and energy deposited on the resist is widely distributed, which varies the size of the resultant resist pattern depending on the density of the pattern. The Exposure Intensity Distribution (EID), when the incident electron beam is directed onto one point (x, y) on the resist applied on the substrate constituted by one material, is generally approximated by a function shown as Formula (1) below, in which a forward scattering element and a backscattering element are expressed as a Gaussian distribution.
                              f          ⁡                      (                          x              ,              y                        )                          =                              1                          π              ⁡                              (                                  1                  +                  η                                )                                              ⁢                      {                                                            1                                      β                    f                    2                                                  ⁢                                  exp                  ⁡                                      (                                          -                                                                                                    x                            2                                                    +                                                      y                            2                                                                                                    β                          f                          2                                                                                      )                                                              +                                                η                                      β                    b                    2                                                  ⁢                                  exp                  ⁡                                      (                                          -                                                                                                    x                            2                                                    +                                                      y                            2                                                                                                    β                          b                          2                                                                                      )                                                                        }                                              (        1        )            
Wherein, βf is a forward scattering length, βb is a backscattering length and η is a backscattering intensity ratio. The values of the forward scattering length βf, the backscattering length βb and the backscattering intensity ratio η depend on electron beam energy, membrane thickness of the resist, the substrate material and so on, and are determined by experiment or simulation. For example, if the membrane thickness of the resist is 0.3 μm and the accelerating voltage of the electron beam is 50 kV, βf=28 nm, βb=11.43 μm and η=0.67. Generally, the forward scattering length βf is a value not limited to pure forward scattering, but includes components such as blurring of the electron beam due to aberration etc. (so-called beam blur) and acid diffusion.
In an existing proximity effect correction method, a pattern shape correction to reduce the linewidth for improvement of exposure margin and dose correction to correct the dose of the pattern in order to obtain a target linewidth at a threshold value Eth of the deposited energy are executed. This kind of proximity effect correction method has been proposed, for example, in Japanese Laid-Open Patent Publication No. 2001-52999 or Japanese Laid-Open Patent Publication No. 11-26360.